A simple automatic titrator based on a digital balance

A computer-controlled automatic titrator incorporating a weight burette is described. The titration vessel is mounted on the pan of a zero-displacement digital balance which records the weight of added sample as well as the weight of titrant added during the titration.     

A new automatic recording titrator and its applications

A new type of automatic recording titrator has been developed. The titrant is added intermittently and the titration curve is recorded stepwise, potential changes being registered in the intervals between deliveries of titrant. The increments of titrant and the intervals can be pre-set, but give the best results if controlled automatically during the titration. The end-point and the volume of titrant consumed are read from the recorded titration curve.     

一种新型气压式滴定仪的研制

介绍一种新型气压式滴定仪的结构、性能、特点及使用方法。该仪器能迅速、准确地加液调零,使用方便,克服了旧式滴定管漏液、取液时易玷污、加液调零较麻烦等缺点,在适当的情况下还可以作为移液管使用。     

Potentiometric flow titration of iron(II) and chromium(VI) based on flow rate ratio of a titrant to a sample

A new potentiometric flow titration has been proposed based on the relationship of the flow rates between titrant and sample solutions. A sample solution is pumped at a constant flow rate. The flow rate of the titrant solution is gradually increased at regular time intervals and a flow rate for the titrant solution in the vicinity of the equivalence point is obtained. The concentration of the sample is calculated by C(S) (mol l(-1))=(R(T) (ml min(-1))xC(T) (mol l(-1)))/R(S) (ml min(-1)), where C(S), C(T), R(S), and R(T) denote the unknown sample concentration, titrant concentration in the reservoir, the flow rate of the sample solution which is a constant rate, and the flow rate of the titrant solution at an inflection point, respectively. The potentiometric flow titration of iron(II) with cerium(IV) and of chromium(VI) with iron(II) has been presented. The titration time of the proposed method is about 10 min per sample. An R.S.D. of the method is 0.77% for seven determinations of 1x10(-3) mol l(-1) iron(II). Similarly, the flow titration of chromium(VI) with iron(II) is carried out over the range 1x10(-4)-1x10(-3) mol l(-1) chromium(VI) and is successfully applied to the determination of chromium in high carbon ferrochromium.     

Multicommutated generation of concentration gradients in a flow-batch system for metronidazole spectrophotometric determination in drugs

The titration by using the perchloric acid as titrant and malachite green as indicator is the classical method for the determination of metronidazole, 2-(2-methyl-nitroimidazol-1-yl) ethanol, in drugs. However, this procedure is slow, laborious and consumes great amount of reagents and samples. Moreover, it requires careful manipulation because the reagents cause irritation in the skin and in the eyes. To overcome these drawbacks an automatic system is proposed. It uses three-way solenoids valves, an open chamber and it exploits concentration gradients generated into the chamber in a multicommutated way. As the proposed system embodies the characteristics of flow-batch systems and of multicommutation techniques in flow, it is here named flow-batch-multicommutated titrator. The system is fully controlled by microcomputer running software written in LabView 5.1 graphic language. It processes 60 samples per hour with relative standard deviation smaller than 2.3% (n=6) and in each titration it consumes 2.5 and 1.5 ml of sample and titrant, respectively. By applying the paired t-test, no statistic differences at the 95% probability level between the results of the proposed system and classical titration were observed.     

Coulometric titration with air transported sample

Air transported samples of a mixture containing the analyte and a supporting electrolyte are consecutively propelled into a microconduit system through a titration cell, a coil and a detector cell. Different amounts of electrochemically generated titrant are obtained in the separate samples while they are passing through the titration cell. Various quantities of the titrant are achieved by changing the duration of the titrant generating process that is done by various time for the sample solution staying in the titration cell (different sample movement rate). The titrated sample is then homogenised in the coil and detected in an electrochemical detector cell that supplies necessary data for the analyte determination. The declared method is experimentally verified on coulometric titration of hydrochloric acid (HCl) with electrogenerated sodium hydroxide and a titration of aniline with bromine generated in a bromide solution.     

Oxidability Determination in Waste Waters Using an Automatic Titrator Based on a Multicommutated Unsegmented Flow System

Abstract

The automatic titrator based on a multicommutated unsegmented flow system was applied to redox titrations and used for oxidability determination in waters analysis. This automatic titrator allows the attainment of complete titration curves, being the determination of titrand concentration performed without requiring any prior calibration. After sample treatment (oxidation step), the oxidability determination in waste water samples was accomplished by the automatic flow titrator (titration step). Repeated determinations of standard solutions gave a 3.5% RSD (n=10, 0.010M) for repeatability and a 3.2% RSD (n=2, 0.057M) for reproducibility. Samples results (n=9) were in good agreement (t-test) with those obtained with a reference procedure.     

Tracer-monitored flow titrations

The feasibility of implementing tracer-monitored titrations in a flow system is demonstrated. A dye tracer is used to estimate the instant sample and titrant volumetric fractions without the need for volume, mass or peak width measurements. The approach was applied to spectrophotometric flow titrations involving variations of sample and titrant flow-rates (i.e. triangle programmed technique) or concentration gradients established along the sample zone (i.e. flow injection system). Both strategies required simultaneous monitoring of two absorbing species, namely the titration indicator and the dye tracer. Mixing conditions were improved by placing a chamber with mechanical stirring in the analytical path aiming at to minimize diffusional effects. Unlike most of flow-based titrations, the innovation is considered as a true titration, as it does not require a calibration curve thus complying with IUPAC definition. As an application, acidity evaluation in vinegars involving titration with sodium hydroxide was selected. Phenolphthalein and brilliant blue FCF were used as indicator and dye tracer, respectively. Effects of sample volume, titrand/titrant concentrations and flow rates were investigated aiming at improved accuracy and precision. Results were reliable and in agreement with those obtained by a reference titration procedure.     

A new approach to flow-batch titration. A monosegmented flow titrator with coulometric reagent generation and potentiometric or biamperometric detection

Monosegmented flow analysis (MSFA) has been used as a flow-batch system to produce a simple, robust, and mechanized titrator that enables true titrations to be performed without the use of standards. This paper also introduces the use of coulometry with monosegmented titration by proposing a versatile flow cell. Coulometric generation of the titrand is attractive for titrations performed in monosegmented systems, because the reagent can be added without increasing the volume of sample injected. Also, biamperomeric and potentiometric detection of titration end-points can increase the versatility of the monosegmented titrator. The cell integrates coulometric generation of the titrand with detection of end-point by potentiometry or biamperometry. The resulting titrator is a flow-batch system in which the liquid monosegment, constrained by the interfaces of the gaseous carrier stream, plays the role of a sample of known volume to be titrated. The system has been used for determination of ascorbic acid, by coulometric generation of I₂ with biamperometric detection, and for determination of Fe(II), by coulometric generation of Ce(IV) with potentiometric detection of the end-point, both in feed supplements.     

Maßanalyse und Katalyse

The application of automatic titration instruments for volumetric determinations using catalytic indicator reactions is described. Examples for a photometric (Mn²⁺ with EDTA), potentiometric (Hg²⁺ and Ag⁺ with KI, I^? with Hg²⁺) and biamperometric (Cu²⁺ with EDTA) regulation of the automatic titrator are given. In some of these methods, contrary to the usual way, it is the inhibitor which serves as a titrant (“titration with the brake”) and not the catalyst.     

Reaktion von Vanadium(IV) mit 3′-Pyridylfluoron und seine photometrische Bestimmung

The application of automatic titration instruments for volumetric determinations using catalytic indicator reactions is described. Examples for a photometric (Mn²⁺ with EDTA), potentiometric (Hg²⁺ and Ag⁺ with KI, I^? with Hg²⁺) and biamperometric (Cu²⁺ with EDTA) regulation of the automatic titrator are given. In some of these methods, contrary to the usual way, it is the inhibitor which serves as a titrant (“titration with the brake”) and not the catalyst.     

全自动电位滴定法测定锂电池原料碳酸锂中主成分的含量

采用全自动电位滴定法测定锂电池原料碳酸锂中主成分的含量,用盐酸标准溶液进行滴定,考虑自动电位滴定仪的灵敏性和准确度,通过多次对比实验,确定了仪器的最佳工作参数、滴定剂浓度和样品称样量等滴定条件;对两个不同品位试样分别进行了11次平行测定,相对标准偏差(RSD)均小于1％.在碳酸锂试样中加入基准物质无水碳酸钠进行碳酸根的...     

A microcomputer-controlled titrator for automated individual analysis

A titration unit for automatic analysis systems is described. The titrator performs different titrations specified by strings of digital parameters. It has 4 independent titration stations with individual electrode systems. A multiburette with 20 cylinders provides all stations with the necessary reagents. End-point titrations, and incremental and equilibrium titrations are controlled by a microcomputer. In combination with a sample transport and a desk calculator, the titrator can be used to process automatically samples of different natures which require different treatment.     

Robust flow-batch coulometric/biamperometric titration system: determination of bromine index and bromine number of petrochemicals

A flow–batch system was constructed and evaluated to perform coulometric titrations with biamperometric end point detection. The flow section of the system is employed for sampling by injecting a sample volume (50–300 μL) in a flow injection-like system. About 1.5 mL of a suitable carrier solution is delivered by a peristaltic pump in order to quantitatively transfer the sample to the system titration cell (2.0 mL total inner volume). The carrier contains the coulometric precursor for the titrant species. The cell contains two pairs of platinum electrodes used for coulometric generation of reagent and biamperometric detection and is actively stirred. The titrant species is generated and the titration is performed by the usual batch procedure with the excess of titrant being detected by biamperometry following the analysis of the titration curve. System operation is computer controlled and all operations are automated, including titration curve analysis and cell cleaning after the titration is ended. The system is characterized by its robustness because its operation does not depend on flow rates, and the work using coulometric methods which generate gases at the counter-electrode is not troublesome. The flow–batch system has been evaluated for determination of bromine index and bromine number (relative to the total reactive olefin content) in petrochemicals according to an ASTM procedure. Typical precision (R.S.D.) is between 0.5 and 6% for different petrochemicals whose bromine number/index vary from 1000 to 10 mg of bromine per 100 g of sample, respectively. Recoveries for standard additions are between 92 and 123% for 10 mg of Br₂ per 100 g increments and 98 to 101% for 100 mg per 100 g increments. Accuracy of the proposed system was evaluated against results obtained by the standard ASTM with no significant difference detected at 95% confidence level.     

Determination of sulphuric acid in process effluent streams using sequential injection titration

Sulphuric acid in process effluent streams from an electrorefining copper plant was analysed with a sequential injection (SI) titration system using sodium hydroxide as titrant. In the proposed SI titration system a base titrant, acid analyte and base titrant zone were injected sequentially into a distilled water carrier stream in a holding coil and swept by flow reversal through a reaction coil to the detector. The base zones contained bromothymol blue as indicator and the endpoint was monitored spectrophotometrically at 620 nm. The influence of carrier stream flow rate, acid and base zone volumes and titrant concentration on the linear range of the method was studied to obtain an optimum. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 0.006-0.178 mol l(-1) of H(2)SO(4) for a NaOH concentration of 0.002 mol l(-1). The results obtained for the SI titration of process samples were in good agreement with a standard potentiometric method with an RSD<0.75% and a sample frequency of 23 samples h(-1).     

Flow injection titration basing on the merging-zone technique

The proposed approach relies on titration of a sample that is gradually diluted in strictly controlled way in the flow injection system developed. On each step of sample dilution equal volumes of the sample and titrant solutions are simultaneously injected into two carrier streams and the zones are merged with each other. Then, they are mixed completely in the mixing chamber, merged with a stream of indicator and directed to a detector. It has been revealed that the method provides the results with accuracy better than ±3.3% (RE) and with mean repeatability lower than 1.0% (RSD). When the analyte concentration in a sample is too low to be determined directly, the procedure of titration with standard addition is exploited. The proposed approach has been successfully applied to the determination of total acidity in vinegars and magnesium and calcium in pharmaceutical products. The results obtained were comparable with those provided by the reference methods. The proposed procedure is characterized by low consumption of sample (usually less than 2 mL), titrant (about 3 mL) and indicator (about 0.6 mL). Average time of a single analysis is similar to time of traditional batch analysis.     

浊度滴定法

报道了一种实用的浊度传感器及浊度滴定仪，以及一种利用此仪器检测溶液的浑浊程度（溶液中散射光相对强度）来判断沉淀反应滴定终点的方法。将一束光线通入溶液，在溶液中与其垂直的方向上，利用内置浊度传感器检测散射光相对强度；随着滴定剂的加入，溶液将渐变得浑浊，散射光相对强度逐渐增强。如果沉淀反应完全且溶解度足够小，散射光相对强度将在化学计量点处达最大值，由此可判断滴定终点。以AgNO3溶液滴定NaCl溶液为例俊证了浊度滴定法，结果表明：浊度滴定法样化学指示剂法适用于更低的浓度；在适当的条件下浊度滴定法的精密度和准确度均可＜0.2%。     

多元校正流动注射电位滴定法同时测定苯甲酸和山梨酸

将流动注射应用于酸碱电位滴定分析,建立了一种可同时测定混合有机酸的电位滴定新方法。在该方法中,用氢氧化钠与氯化钾的混合溶液作为滴定剂,在流通池中同时插入pH指示电极和氯离子指示电极,在滴定过程中的任一滴定点,流出液的pH值和酸碱的混合比例可由两个电极的电位测定值同时获得,从而可应用多元校正法由相应的滴定曲线求得混合酸中每一种组分的含量。该方法不仅免去了体积和时间读数,而且减少了试剂和样品的消耗量,分析速度快。应用该方法对混合样品中的苯甲酸和水杨酸进行同时测定,其相对标准偏差分别为0．19％～0．37％,回收率分别为97．3％～102．6％。     

An automatic back titration method for microchemical analysis

An automatic back titration method for microchemical analysis is introduced, which is based on conventional volumetric analysis's principle and the use of flow injection analysis apparatus for the automation and microminiaturization of the process. The sample and a known, but excess amount of a calibrated reagent solution are injected and propelled into a titration cell, where their reaction takes place. The excess of the reagent is then titrated with a titrant containing an indicator and the end point is monitored photometrically. Since homogeneous mixing in the titration cell is obtained magnetically in the whole process, there is a linear relationship between the analyte's concentration and the volume of the titrant consumed. Nickel in the range of 10-70 g 1(-1) is determined by the above method, in which 30 microl of sample and 500 microl of EDTA are injected and the excess of EDTA is titrated with a standard zinc salt solution containing xylenol orange which could be blocked by nickel ion in a direct titration. This method is characteristic of low sample and reagent consumption, high sampling rate as high as 45 samples h(-1), negligible effect of sample's viscosity, small carry-over effect (lower than 0.14%), and very good precision, whose relative standard deviations are as small as 0.24%.